This invention relates generally to knot tying mechanisms, and specifically to an improved billhook and actuation means therefor.
In conventional hay balers, hay, straw and similar crop material that has been previously cut, windrowed or swathed is picked up from the ground by a pick-up unit and fed in successive batches or charges into an elongated bale chamber in time sequence with a reciprocating plunger. The plunger compresses the material into bales and, at the same time, gradually advances the bales towards the outlet of the bale chamber. As the bales reach a predetermined length as determined by a metering device, a knotter is actuated which wraps cord, twine or other similar tie material around the bale and secures the ends of the material together.
In a typical baler a knotter is mounted on the bale chamber above a slot therein, the knotter comprising a twine holder from which twine extends to encircle a bale. During the baling operation, the leading strand of twine is held by the twine holder and extends forwardly across a twine retainer finger and a billhook and then in front of the bale. The twine retainer finger supports the strand so that it does not bear forcefully against the billhook. A needle is involved in completing the encirclement of twine around the bale and when advancing, the needle lays a trailing strand across the twine retainer finger, billhook and twine holder. A twine finger captures these strands of twine and positively positions the strands against the heel of the billhook. Thus, there are presented in a certain zone a pair of twine portions of strands lying along side of each other and these portions are twisted into a bight by the billhook and a portion thereof is pulled through the bight to form a double overhand knot. On completion of the operation of the knotter, the twine finger returns to the initial position. Removal of the tied knot from the billhook involves mechanical stripping by a movable member which normally embodies a knife operable to cut the twine from the twine supply so that the tied bale is complete in itself. The tying mechanism thus includes several components working in a precisely timed relationship so that theoretically the mechanism ties one knot for each bale and prepares the twine for the succeeding bale.
A knotter is inherently a relatively complicated structure, and the precisely timed operation thereof suffers at times from faulty operation. This may be due to the vibrations of the baler, the tension in the twine and the jarring of the baler as it moves through the field. The crop may be tough or resilient causing the strands of twine to jump about. Variations in the baling twine also affect the knotting operation. Balers are operated outside and often parked in the field, whereby the knotter is exposed to all weather conditions. Also, the knotter is subjected to dirt, crop and debris resulting in abrasion and interference of operation.
At present, balers are capable of reasonably efficient operation at speeds up to a maximum of approximately eighty to ninety strokes per minute of baling plunger. One reason for this limitation on the operation speed is that the presently available knotters cannot perform the complex tying operation at faster speeds, and the latter operation must be carried out in timed sequence with the strokes of the baling plunger. Restraint on faster knotter operation is imposed by various cam and cam followers, complicated knotter drive means, and other oscillatory parts employed in a typical knotter which give rise to relatively high inertia forces.
In some known knotters the billhook may comprise two jaws with one being movable relative to the other to effect opening and closing of the jaws. The movable jaw may be provided at its heel with a roller which acts as a cam follower and engages a cam track having a profile appropriate to the required action of the jaws. Invariably, the profile of the cam track is relatively complex, and, therefore, expensive. Also, the track has to be accommodated within the knotter mechanism and the size and shape is not always easy to tolerate in this respect. The provision of a roller on a movable jaw of the billhook gives rise to another problem in that the movable jaw serves as a twine guide in the knotting sequence and the roller, in conjunction with the associated spindle tends to create a twine trap which can lead to a knotter malfunction.